DEAR ABBY: I'm writing this a few days before I go into surgery for something I never thought was a big deal. Melanoma.

I had a flat "unthreatening" mole on my arm -- sort of a large freckle -- that had been there for as long as I could remember. Not too long ago, it started growing quickly enough that I began to notice the difference from one week to another. I didn't worry about it because I have freckles all over. Fortunately, a friend of mine who is a dermatologist said, "You ought to have that looked at."

My doctor biopsied the freckle and said he was 90 percent certain it was nothing to worry about. A few days later he called me himself and informed me I would need a complete body exam, my lymph nodes examined, and further surgery to take more skin off that arm.

I quickly learned that unlike less serious skin cancers, melanoma has a very high rate of metastasis. It can quickly spread to the lymph nodes, the eyes, the stomach, even to the brain. It is one of the fastest-growing cancers in the United States as far as numbers of people affected. It can kill you, and once you've had it, you are at risk for the rest of your life. It is so serious that I will have trouble getting life insurance and will no longer be allowed to give blood.

Sun exposure is one of the risk factors for melanoma. I grew up in the sun -- sailing, swimming, on the beach. I've even occasionally used tanning beds. I won't be doing that anymore.

Please, Abby, tell your readers how serious melanoma is. They should watch for any changes in moles and have them checked immediately.

I'm 41, and my doctor tells me he's seen it in people as young as 20. It tends to strike younger people than other cancers do. When I think of the tans I worked so hard to get, and the sunburns I shrugged off and slathered with aloe, I cringe. If I could turn back the clock I would, and stay lily-white. -- LAURA H. MARSHALL, WALNUT CREEK, CALIF.

DEAR LAURA: Thank you for your important warning. Everyone is at risk for skin cancer, regardless of his or her skin color. Summer is just around the corner, and I pray that my sun-worshipping readers will remember a few tips to protect themselves from ultraviolet (UV) rays.

About 80 percent of skin cancers could be prevented by protecting ourselves from the sun's rays. Limit direct sun exposure, especially during midday. Cover up -- wear long sleeves and a hat. Use a sunscreen with a sun protection factor (SPF) of 15 or higher. Be sure to wear sunglasses that block UV rays. Avoid sunlamps and tanning booths, and check your skin regularly for any changes in freckles or moles.

Some medications, such as antibiotics, can increase the skin's sensitivity to the sun, so ask your physician or pharmacist about the drugs you are taking and take extra precautions.

And remember: Babies and small children are subject to the same eye and skin problems that adults are when exposed to the sun. So, parents, make sure your youngsters' eyes and skin are protected, too, when you take them for a stroll, out to play or shopping. Their safety depends on you.